Thrombopoietin in Patients With Congenital Thrombocytopenia and Absent Radii: Elevated Serum Levels, Normal Receptor Expression, But Defective Reactivity to Thrombopoietin
Matthias Ballmaier,
Harald Schulze,
Gabriele Strau
,
Klara Cherkaoui,
Nicole Wittner,
Stefanie Lynen,
Susanne Wolters,
Jakob Bogenberger, and
Karl Welte
From the Department of Pediatric Hematology and Oncology, Medical School Hannover, Germany and Amgen Inc, Thousand Oaks, CA. The first two authors contributed equally to this work.
The pathophysiology of thrombocytopenia in the syndrome of thrombocytopenia with absent radii (TAR) is not yet understood. We examined thrombopoietin (TPO) serum levels and the in vitro reactivity of platelets to TPO in five patients affected with TAR syndrome. We found elevated TPO serum levels in all patients tested, excluding a TPO production defect as cause for thrombocytopenia in TAR syndrome. In addition, we found similar expression of the TPO receptor c-Mpl on the surface of platelets from TAR patients (5 of 5) and a similar molecular weight of the receptor as compared with healthy controls (4 of 4). Platelet response to adenosine diphosphate or thrombin receptor agonist peptide SFLLRN (TRAP) was normal in TAR patients. However, in contrast to results with healthy controls we could show absence of in vitro reactivity of platelets from TAR patients to recombinant TPO as measured by testing TPO synergism to adenine diphosphate and TRAP in platelet activation. TPO induced tyrosine phosphorylation of platelet proteins was completely absent (3 of 4) or markedly decreased (1 of 4). Our results indicate that defective megakaryocytopoiesis/thrombocytopoiesis in TAR syndrome is not caused by a defect in TPO production but a lack of response to TPO in the signal transduction pathway of c-Mpl.
Blood, Vol. 90 No. 2 (July 15), 1997:
pp. 612-619
© 1997 by The American Society of Hematology.
